Core B: Neuropathology and Tissue Culture Core JC virus (JCV) is well known as the cause of the human demyelinating disease progressive multifocal leukoencephalopathy (PML). In animals and in humans it has been associated with the production of brain tumors, most likely through mechanisms involving T-antigen a product of the JCV early genes. In human medulloblastomas, a frequent malignant brain tumor of children, our laboratory has also demonstrated JCV DNA and T antigen protein using PCR and immunocytochemistry. We have also developed a murine model of medulloblastoma in mice transgenic for the JCV archetypal early genes (JCV-CY mice). Because of the parallels between the human tumors and murine model, this program project proposes to focus on medulloblastomas and the relationship to JCV pathways. Within the overall project, Core B will perform pathologic evaluation of animals, tumors, and primary cultures from tumors generated by Core Component A: Experimental Animal Core. Core will also derive cell lines from primary tumor tissue and supply the individual projects with the necessary tissue and cell lines. This Core will contribute to the program project by providing a systematic, consistent and reliable mechanism for the tissue based analysis of the experimental animals, tumors and cell cultures utilized in the experiments. Integrating the pathologic and cell culture expertise with Projects 1,2 and 3 plus Core A will ensure that handling, storage and analysis of these specimens and cells is uniform and efficient.